hanging loop

[waynewagner33]

I was wondering if it was possible to connect a garn straight to my existing system I have three zones each one has its own pump. im trying to figure out if I can connect garn directly to system and depressurize it .my second floor heating zone will be above garn unit itself but if I can bleed that zone it would create a siphon since return is lower. I already have a dhw tank and this would be ideal for me because I belive I would only need to connect the two lines and done with piping. if anyone has any ideas on how I could start siphon that would be helpful also if there is any disadvantages to this I would like to hear. I think it could work and would save me the cost of heat exchanger and extra work any ideas please chime in

 

[ewdudley]

I've never seen it but from what I read it can be done. The problem is that valve stems, threaded joints, and bleeder valves can all have leaks that are so small they won't leak any water out under low pressure because of the surface tension and viscosity of water, but over time they can draw in air under vacuum because of the low viscosity of air. If you're lucky there won't be any such leaks and it would work just fine. (To seal suspected small vacuum leaks, applying Permatex can often work very well.)

Also gas will tend to come out of solution wherever pressure is the lowest, but gas also comes out of solution where temperature is the highest, so with Garn there might not be enough dissolved gas leaving the boiler to cause a problem.

To get rid of air you would need to valve-off the Garn, pressurize the system with make-up water (presumably the existing make-up valve and regulator will still be available), and then bleed off air at high points. Then run the system for a while and repeat the process until no more air is found. And then repeat the process as the months go by to see if there's a problem.

Hopefully water treatment that is good enough to protect boiler will be good enough to protect your system, but you would need to make sure.

 

[waynewagner33]

so do u think it would be a good idea the difference in elevation would be under 5 ft do u think that would be to much vacuum what would u think I could go before loop collects air if it was a once in 6 month thing I wouldn't mind but once a week could be crazy

 

[ewdudley]

so do u think it would be a good idea the difference in elevation would be under 5 ft do u think that would be to much vacuum what would u think I could go before loop collects air if it was a once in 6 month thing I wouldn't mind but once a week could be crazy

Yeah, I think it would be a good idea, but I don't have any first-hand experience and I'm just passing on reports of success. If I remember correctly Tom from http://www.americansolartechnics.com/ was telling about one or more systems that used hanging loops with no problem, maybe you could look him up and pick his brain. I doubt you would need to remove air even once a year once you got it sorted out, I'm just saying it's not as fool proof as a normal pressurized heating loop and there might be some leaks to deal with in the beginning. As you suggest, only dealing with 5 ft is especially encouraging.

In any event you would need to stay on top of the water testing and water treatment requirements to protect both boiler and system.

Just an idea: If upstairs load is pretty small, run a separate pressurized loop from the upstairs to a sidearm by the Garn, or a copper loop inside the Garn.

 

[maple1]

What about something that would be low-pressure, rather than no-pressure?

Thinking along the lines of an open expansion tank that is higher than all the rest of the system, but connected by a longish run of small pipe that would allow water to come & go from it OK but maybe help limit air invasion. Like maybe, well insulated in the attic?

Most circ pumps spec 4psi or so for inlet pressure - so an open expansion tank 10' above the circ pumps & plumbed in right before them would give the pump 5psi or so from static column. Not sure how the Garns are spec'd on pressures though - maybe an open expansion tank at the same height as the highest system point? My boiler manual specs an open expansion tank should be 8' above the system high point.

 

[ewdudley]

Thinking along the lines of an open expansion tank that is higher than all the rest of the system, but connected by a longish run of small pipe that would allow water to come & go from it OK but maybe help limit air invasion. Like maybe, well insulated in the attic?

I believe an important part of an open-to-atmosphere expansion cistern is that there has to be a fairly large pipe (like about 1.25" for a 100,000 to 150,000 btu per hour boiler) that goes from the boiler up over into the top of the expansion cistern so the system can blow, spit, and gurgle insead of splitting seams while trying to blow steam through a half inch pipe a hundred feet away.

For a Garn this would mean sealing off the man-hole and extending a fat pipe up into the top of an open tank in the rafters, plus a small pipe from below the water level to carry expansion water to the bottom of the tank. Whether or not Garn agrees, it would probably void the warranty.

 

[maple1]

I forgot just how open the Garn is with that manhole thing they have. IMO if they could adapt their unit to a pressurized scenario they would broaden their appeal a lot - likely a lot involed in getting to that point though.

My boiler manual also shows, in the open tank setup, just a pipe going from the top of the boiler to the bottom of the elevated open tank. Plus a vent out the top of the tank, of course - or two actually, one going up high for air movement and one running back down I assume to drain in the case of too much expanding water. It specs 1/2" copper for tank connection & doesn't seem to differentiate in that between open & closed tanks - that kind of open tank setup must be quite common in Europe?

And the more I look at it, it seems to also be OK with what I ended up for an expansion setup - a non-bladder closed expansion tank sitting on the floor beside the boiler. Or at least it doesn't spec a bladder that I can see - although a bladder would no doubt be a better setup from the air 'infiltration' perspective.